In a connection plug that connects interconnection materials or interconnections of a semiconductor device, low-resistance metals such as Cu or Al are used. With the scale down design of semiconductor devices moving ahead, the cross sections of interconnections and interconnection plugs decrease. As a result, the following phenomena have become more serious:
(1) Increase in the resistance values of interconnections and connection plugs
(2) Electromigration of metal ions by current densities which have increased and
(3) Stress migration due to heat cycles during manufacturing and heat generation etc. during working.
Electromigration and stress migration pose problems, such as changes with time in the resistance of metal interconnections and connection plugs and disconnections of them.
In order to prevent interconnections from being broken due to electromigration, there is available a method which involves using two materials in combination: an interconnection material A which has a low resistance value but is not resistant to migration (for example, Cu or Al) and an interconnection material B which has a high resistance value but is resistant to migration (for example, titanium, tungsten and suicide materials of these metals). In this case, the disconnection of interconnections can be prevented by the redundancy effect of the interconnection material B. However, this method is effective for interconnections although it is not effective for connection plugs. Also, although interconnections do not lead to disconnections, there is a problem that the interconnection resistance increases. Furthermore, this method is not effective for stress migration.
In contrast, there has been proposed a semiconductor device element in which carbon nanotubes having resistance to electromigration are used in connection plugs (Japanese Journal of Applied Physics, Vol. 41, pp. 4370 to 4374, 2002).
In this example, carbon nanotubes are formed in via holes and used as connection plugs that connect an upper interconnection layer and a lower interconnection layer together. Approximately 1000 carbon nanotubes are formed in a via hole of 5×30 micrometers square.
It is known that carbon nanotubes have high migration resistance and hence migration does not readily occur in carbon nanotubes.
When methods that involve combining interconnection materials are adopted, it is impossible to prevent the occurrence of voids due to the electromigration in connection plugs. Also, in interconnections, it is impossible to prevent changes in resistance that are caused of the disconnection of part of the interconnections due to electromigration or stress migration.
However, the reason why connection plugs formed from multilayer carbon nanotubes have high resistance values in spite of the fact that the multilayer carbon nanotubes have metallic properties and low resistance is that the contact resistance between the carbon nanotubes and the metal interconnections is high, with the result that the resistance of connection plugs increases due to the contact resistance even when the resistance of the carbon nanotubes is low.
The present invention provides an interconnection structure of a high-reliability semiconductor device which has a low resistance value even in the case of scale down design and does not produce electromigration and stress migration, and a method of manufacturing the interconnection structure.